(a) Field
The present disclosure relates to a power transmission apparatus for a hybrid electric vehicle.
(b) Description of the Related Art
Environmentally-friendly vehicle technology is an example of the core technology that controls the future of the automobile industry, and advanced car makers have focused their energy on the development of an environmentally-friendly vehicle to meet environmental and fuel efficiency regulations.
In particular, car makers have developed an electric vehicle (“EV”), a hybrid electric vehicle (“HEV”), a fuel cell electric vehicle (“FCEV”), and the like, as future vehicle technologies.
Because such vehicles have various technological restrictions such as a weight and cost, the vehicle makers have turned to the hybrid electric vehicle as a way to meet exhaust gas regulations and improve fuel efficiency performance, and have entered into keen competition for commercializing the hybrid electric vehicle.
The hybrid electric vehicle is a vehicle using two or more power sources. The power sources may be combined by various methods. For instance, the power sources may include a motor/generator driven by electric energy and may also include a fossil fuel engine, such as either a gasoline engine or a diesel engine.
The hybrid electric vehicle generally uses, as a primary power source, both (i) a motor/generator having a relatively excellent torque at low speeds and (ii) an engine having a relatively excellent torque at high speeds.
At low speeds, the hybrid electric vehicle's operation of the fossil fuel engine stops, and the motor/generator is used instead. As a result, the hybrid electric vehicle can provide high fuel efficiency and a reduction of exhaust gas.
A double clutch transmission (“DCT”) is an example of a transmission useful in a hybrid electric vehicle. A DCT includes two clutches applied to a manual transmission scheme, and thereby enhances efficiency and convenience.
The DCT uses two separate clutches for odd-numbered shift-stages and even-numbered shift-stages, and thereby improves continuity in torque transmission by alternatingly operating these two clutches.
However, in some scenarios when starting a vehicle, such as starting a vehicle on a slanted surface (which can cause a rearward slip of the vehicle), use of the DCT results in a relatively high degree of clutch wear and energy loss. In addition, the DCT typically is controlled with a short shift-control period due to low heat capacity, which can easily cause shift shock to occur.
In addition, in order to use a DCT in a hybrid electric vehicle, an appropriate arrangement of a motor/generator as a power source must be devised.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the present disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.